Standalone Signal Source

When I first designed the ZLPLL board I had 2 target applications in mind: (1) as a local oscillator board, and (2) as a standalone signal source to aid receiver alignment or testing of power amplifiers.

So I finally had time to take one of my development boards, put a box around it and its own power source so that I can use it in the field or loan it out to others to help them setup and test their station.

The case I chose was a Jaycar HB5067 die-cast aluminium box which gives just enough room for a 2S lithium battery cell (1300mAH 7.4V)

The thumbwheel switch feature allows 10 present frequencies to be selected – in my case they are 50KHz from the common SSB calling frequencies on my most active bands: 2m, 70cm, 33cm, 23cm, 13cm, 9cm, 6cm and 3cm.

Full output power (> +5dBm) across a wide frequency range is not possible with just a single inductor on the ZLPLL board, therefore as an experiment the higher value inductor for frequencies below 1GHz was fitted to just one output and the standard 3.9nH inductor left on the 2nd output.

This facilitates both high and low frequency operation from the same board by simply swapping to the correct output connector. There were no stability issues observed as long as the unused port was terminated, and a secondary benefit is the output power level increases by 2 or more dB as the power is no longer split between 2 output ports.

Inside View

Now I sure wish I had done this sooner, as this box is now a valuable addition to the “field day” kit for checking receivers are actually working, and on frequency (often I forget to change IF frequency on my FT817 radio which as caught me out a few times)

The lithium battery keeps the board running for around 4 hours between charges. The battery has to be removed for charging with a balanced charger (such as the iMax B6 which I use, or the Jaycar one) which is a minor inconvenience.

The self-contained signal source is a perfect companion to any of the WA5VJB PCB log periodic antennas.

To add a professional touch I quickly drew a label in Visio which was laminated and attached to the case using 3M spray adhesive.

The day after building this I needed to test a suspect mini circuits mixer which required a 2nd signal generator. Instead of lugging my 2nd HP signal generator from upstairs to my garage, the signal source was put to use to provide a 144MHz signal for testing the mixer. The mixer was unfortunately dud, but it demonstrated how handy this is for my go-no-go test application.

With the summer months looming this will now live in my portable equipment box ready for the next field day or DX opening.